Traditionally, the tobacco industry has prepared tobacco for storage by overdrying, cooling, and reordering (remoistening) the tobacco on a continuous basis. The reordering, traditionally, is carried out by exposing the tobacco to steam introduced into a reordering chamber. There has been a reluctance to use water to avoid staining of the tobacco. The problem is that steam tends to not only increase moisture content but also tobacco temperature. The control for moisture content includes a moisture sensing device which senses tobacco moisture and, as the temperature increases the tobacco tends to dry more, so the sensor calls for more steam, establishing an upwardly directed temperature spiral. To prevent this, it is conventional to hold down temperature by introducing fresh air into the reordering chamber, responsive to a temperature measuring device measuring the tobacco temperature. The incoming fresh air is effective in holding down tobacco temperature, but it has the undesirable effect of wasting heat and energy, thereby reducing reorder efficiency.
A number of variations for conditioning tobacco have been disclosed in the prior art. One such apparatus is shown in Psaras U.S. Pat. No. 4,091,824. In the method and apparatus of this patent, the tobacco is conditioned by subjecting it to drying at first and second locations, to cooling at a third location, and to reordering at successive fourth and fifth locations, the fourth location employing downdraft and the fifth section updraft. In both the fourth and fifth sections, the reordering is carried out by a combination of steam and water. The patent is concerned primarily with apparatus for establishing laminar flow across the surface of a conveyor for the tobacco and details of control in the reordering sections are not disclosed. It is not indicated how either overheating or staining of the tobacco is avoided, if at all.
The Strydom U.S. Pat. No. 4,336,660 shows an apparatus for drying tobacco products such as cut rag, in which the same is subjected to moisturizing in a chamber upstream of the dryer and cooler. The purpose is to establish a constant temperature and moisture content prior to drying. In the upstream moisturizing section, both steam and water are employed, wherein the moisture is added in response to a moisture meter reading, and the temperature is kept constant in response to a temperature sensor by varying the ratio of steam and water used. Both the moisture and temperature sensors are upstream of the steam and water inputs, so that the control is feed-forward rather than feed-back. It is not indicated in the patent how staining of the tobacco is avoided, nor that this is even a problem in the method and apparatus of the patent.
In the method of the patent, a critical aspect is maintaining a constant mass flow rate. Thus, the method and apparatus of the patent would not be automatically responsive to changes such as change of grade of tobacco.
A similar disclosure is contained in U.S. Pat. No. 4,346,524, to Wochnowski et al, showing a moisturizing unit upstream of a dryer.
An object of the present invention is to control more efficiently the moisture content and temperature of a bed of tobacco, other objects being to avoid staining of the tobacco by water, and to provide an apparatus and method easily responsive to changes such as changes in tobacco mass flow rate, grade of tobacco, or kind of tobacco.